Inline inspection of photovoltaics for electrical defects

ABSTRACT

A method of inline inspection of photovoltaic material for electrical anomalies. A first electrical connection is formed to a first surface of the photovoltaic material, and a second electrical connection is formed to an opposing second surface of the photovoltaic material. A localized current is induced in the photovoltaic material and properties of the localized current in the photovoltaic material are sensed using the first and second electrical connections. The properties of the sensed localized current are analyzed to detect the electrical anomalies in the photovoltaic material.

FIELD

This application claims all rights and priority on prior pending U.S.patent application Ser. No. 11/690,809 filed Mar. 24, 2007. Thisinvention relates to the field of photovoltaics. More particularly, thisinvention relates to the inline inspection of photovoltaic films.

BACKGROUND

Photovoltaics can be made from a variety of different materials and byway of a variety of different processes. One of the more promisingfabrication methods—from a cost standpoint at least—is to formcontinuous webs of photovoltaic material that are sequentially processedas the web moves along a production line. Thus, various layers of thephotovoltaic devices are sequentially formed, one on top of another, asthe web of built-up material progresses down the moving production line.Another fabrication method is to deposit the photovoltaic film on plateglass, which is the preferred method to fabricate CdTe solar cells.

In the past, electrical defects in the photovoltaic film have beenstudied by removing a sample from the production material and inspectingthe sample offline. Removing a sample often introduces serious defectsnear the edges of the remaining photovoltaic material where the samplewas removed.

Further, examining the sample offline means that the information cannotbe readily used in an automatic feedback loop for control of the filmdeposition processes. Further, such offline testing is time consuming,which results in a potential greater loss of material, in the event of aprocess excursion.

What is needed, therefore, is a system that overcomes problems such asthose generally described above, at least in part.

SUMMARY

The above and other needs are met by inline inspection of thephotovoltaic film for electrical anomalies without removing samples. Afirst electrical connection is formed to a first surface of thephotovoltaic material, and a second electrical connection is formed toan opposing second surface of the photovoltaic material. A localizedcurrent is induced in the photovoltaic material, and properties of thelocalized current in the photovoltaic material are sensed using thefirst and second electrical connections. The properties of the sensedlocalized current are analyzed to detect the electrical anomalies in thephotovoltaic material.

In various embodiments according to this aspect of the invention, atleast one of the first electrical connection and the second electricalconnection is formed using a physical contact to the photovoltaicmaterial. In some embodiments, at least one of the first electricalconnection and the second electrical connection is formed using anon-physical contact to the photovoltaic material. In yet otherembodiments, the first electrical connection is formed using at leastone of a laser and an electron beam.

According to another aspect of the invention there is described a methodof inspection by applying an ultraviolet probe laser to a location ofthe photovoltaic material, where the probe laser is applied at a probeenergy sufficient to emit photoelectrons from a conduction band of thephotovoltaic material into a vacuum environment, but the probe energy isinsufficient to substantially excite electrons from a valence band ofthe photovoltaic material into a vacuum environment, and simultaneouslyapplying a visible pump laser to the same location of the photovoltaicmaterial, where the pump laser is applied at a pump energy sufficient toexcite photoelectrons from the valence band of the photovoltaic materialto the conduction band, but the pump energy is insufficient tosubstantially emit photoelectrons from the conduction band of thephotovoltaic material into the vacuum environment, sensing thephotoelectrons that are excited into the vacuum environment to measure acurrent, and interpreting fluctuations in the current as electricalanomalies as a function of position on the photovoltaic surface.

In various embodiments according to this aspect of the invention, thephotovoltaic material does not include a contact film at the location ofthe application of the probe laser. In some embodiments, the probe laseris applied to a first side of the photovoltaic material and the pumplaser is applied to a second side of the photovoltaic material.

In other embodiments, both the probe laser and the pump laser areapplied to a first side of the photovoltaic material through atransparent port into the vacuum environment, where an interior surfaceof the transparent port is coated with a transparent conductive materialthat is disposed in proximity to the photovoltaic material sufficient toreceive and sense the photoelectrons emitted from the photovoltaicmaterial, and the transparent conductive material is disposed insections on the transparent port, where the sections are electricallyisolated one from another, thereby enabling separate measurement of theemitted photoelectrons based on a position of the photovoltaic materialfrom which the photoelectrons are emitted, and the probe laser furthercomprises multiple probe lasers, one each of the multiple probe lasersdedicated to simultaneous irradiation of the photovoltaic materialthrough an associated section of the transparent conductive material.

According to yet another aspect of the invention there is described amethod of inspecting continuously moving photovoltaic material forelectrical anomalies without stopping the movement or removing samples,by forming electrical connections to the photovoltaic material, andinducing either via electron beam or light beam a first localizedcurrent in the photovoltaic material with a first stripe source, sensingthe first localized current at a first time, and likewise inducing asecond localized current either via electron or light beam on thephotovoltaic material with a second stripe source, sensing the secondlocalized current at a second time, where the first stripe source ispositioned downstream along the moving photovoltaic material from thesecond stripe source, and the first stripe source and the second stripesource are oriented at a non-zero angle relative to one another,analyzing properties of the first and second localized currents todetect the electrical anomalies in the photovoltaic material, anddetermining positions of the electrical anomalies in the photovoltaicmaterial based at least in part on a time difference between the firsttime and the second time and a measure of the non zero angle between thefirst and second stripe sources.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are apparent by reference to thedetailed description when considered in conjunction with the figures,which are not to scale so as to more clearly show the details, whereinlike reference numbers indicate like elements throughout the severalviews, and wherein:

FIG. 1 is a first embodiment for a non-physical method for makingelectrical contact with a film, according to the present invention.

FIG. 2 is a first embodiment for illuminating a film, according to thepresent invention.

FIG. 3 is a second embodiment for illuminating a film, according to thepresent invention.

FIG. 4 is a third embodiment for illuminating a film, according to thepresent invention.

FIG. 5 depicts an embodiment for the flow of electrons through a firsttype of photovoltaic material in both the presence of a shunt and innormal operation of the photovoltaic material, when a probe and pump areapplied to the material.

FIG. 6 depicts an embodiment for the flow of electrons through a secondtype of photovoltaic material in both the presence of a shunt and innormal operation of the photovoltaic material, when a probe and pump areapplied to the material.

DETAILED DESCRIPTION

According to the several embodiments of the present invention, there isdescribed a system 10 to perform an inline inspection for electricaldefects of various kinds in a photovoltaic thin film 12, as depicted inFIG. 1. The photovoltaic 12 could be one or more of a variety ofdifferent kinds, such as Cu(In,Ga)Se, Cu(In,Ga)S, or any member of thisfamily of chalcopyrites, or CdS, CdSe, CdTe, or any member of thisfamily of materials, or amorphous silicon.

In one embodiment, the inspection is performed using a beam 14, which iseither an optical beam (optical beam induced current) or, if thematerial 12 is under vacuum, and electron beam (electron beam inducedcurrent). Regardless of the type of beam 14 used, the beam 14 induces acurrent in the photovoltaic 12.

If the material 12 is moving, as in the case of film deposition on amoving web of material during manufacture, the beam 14 is preferablyrastered back and forth across the material 12, normal to the directionof movement of the material 12, to produce an x, y scan 16 of thesurface of the material 12, where x is in the direction of the motion ofthe material 12. This movement of the beam 14 can be accomplished bymoving either the beam 14 source, or directing the beam 14 itself backand forth, such as by a moving mirror for optical beam induced currentor by a changing magnetic or electrical field for electron beam inducedcurrent. Alternately, the photovoltaic material 12 could be movedrelative to the beam 14.

Alternately, the beam 14 remains stationary relative to the width of themoving material 12, so as to sample a single strip along the length ofthe material 12, and the data collected is used for feedback to the filmdeposition processes. However, this embodiment does not allow for repairof the material 12 by laser ablation, as described hereafter. In yetanother embodiment, multiple beams 14 could be used to sample multiplestrips along the length of the material 12.

The top conductor illuminated by the beam 14 is, in one embodiment, thetransparent conducting oxide that is typically formed on a photovoltaicdevice, such as zinc oxide or indium tin oxide. The opposite side of thematerial 12 would then be the conducting substrate, such as stainlesssteel. The variation in the current produced by the photovoltaic 12 asinduced by the beam 14 is used to detect electrical non uniformities inthe film 12 as a function of position.

Electrical contacts 18 or 22 are preferably made between an ammeter 20or other current sensing instrumentation and both sides of thephotovoltaic 12 to detect the current that is induced by the beam 14.The electrical contacts 18 and 22 can be made using either a method thatdoes not physically contact the material 12, or one that does physicallycontact the material 12, or a blend of both methods.

For example, one method of making physical contact with a moving web ofmaterial 12 is by using conducting brushes 18 a that drag on thesurfaces of the material 12 as the material 12 moves relative to thebrushes 18 a. Another method is to use a conductive roller 18 b. Yetanother method is to have a conductive physical probe 18 c that moveswith the material 12 for a period of time, is then raised, repositioned,and lowered again to make contact in a different position of thematerial 12.

When electron beam induced current is used, the electron beam 14 itselfmay be used as a non-contact upper electrical connection, forming eithera positive or negative contact depending on the landing energy employed.If desired, two or more electron beams could be used, one for probingthe material, and the second for making positive or negative electricalcontact. In this embodiment, one or more of the physical contact methods18 could be used for the electrical connection to the bottom of thematerial 12, or some non-contact method could be used.

An alternate method for making electrical contact without physicallytouching the film 12 is to use a contained plasma or corona 22. In thiscase, the film 12 passes by a relatively thin plasma or corona region,which is preferably isolated from the rest of the environment, whetherthat be a vacuum chamber or open atmosphere. This region can be confinedsuch as with a rectangular box 22 running across the length of thematerial 12, containing the necessary field for plasma or coronageneration, and having a pressure that is different from the rest of theinspection device 10.

Optical beam induced current can be performed on a moving film ofmaterial with one or two light beams 14 a and 14 b, as depicted in FIG.2. In one embodiment, these beams 14 a and 14 b run across the material12 in opposite diagonal orientations, allowing for localization of anydefect. The beams 14 a and 14 b are modulated in one embodiment, to gainadditional information from the measurement. FIG. 2 depicts anembodiment where light beams 14 a and 14 b simultaneously illuminate alarge swath of the material 12. Defects are imaged along the moving axisof the material 12, and localized on the material 12 due to thedifferent orientations of the two beams 14 a and 14 b. This method tendsto be faster than scanning each beam 14 a and 14 b as a point across thewidth of the material 12. Scattered light from beams 14 a and 14 b couldalso be used to detect non-electrical defects during any point of thefilm deposition process, including defects on the bare substrate.

The time difference between anomalies as produced by the two beams 14 aand 14 b as the material 12 proceeds along its path of motion indicateswhere across the width of the material 12 the defect resides. Forexample, a defect in the material 12 that is located at a point in thematerial 12 where the beams 14 a and 14 b are relatively close to oneanother would produce electrical events that are relatively closertogether in time, while a defect in the material 12 that is located at apoint in the material 12 where the beams 14 a and 14 b are relativelyfar apart would produce electrical events that are relatively fartherapart in time. With knowledge of the angle between the beams 14 a and 14b and the speed of the material 12, the location of the anomaly in thematerial 12 can be determined.

Electrical isolation of the inspected region can be provided by scribingaway a line of the transparent conducting oxide contact to effectivelysegment the material 12 into electrically isolated regions. Alternately,it may be possible to rely on the sheet resistance of the transparentconducting oxide. The sheet resistance is typically about ten ohms persquare, but in one embodiment, a very thin layer with a much highersheet resistance is formed, as in the deposition of a zinc oxide film onCu(In,Ga)Se material, then the inspection is performed, and finally theremainder of the transparent conducting oxide is formed, as in thedeposition of a final aluminum doped film of zinc oxide.

Finding electrical defects while keeping up with the speed of a movingweb of material 12 is best performed using relatively high dataacquisition rates. A high speed time delay and integration acquisitionsystem is used in one embodiment to acquire the induced current data.Analysis of the data may require a measurement of the current-voltagecurve at each scan point. Weak diode or shunting defects are localizedin one embodiment to within an area of about two millimeters in diameterand then electrically isolated from the remainder of the surface bylaser ablation. In one embodiment the beam 14 sources preferablyilluminate the web 12 between two parallel strip conducting brushes 18,not depicted in FIG. 2.

Some embodiments of the invention are especially beneficial for findingOhmic shunts in the material 12, which drain photocurrent from the loadunder any voltage bias, and also for finding weak diodes in the material12, which drain photocurrent from the load while under forward bias.Locating the positions of the worst shunts (the word “shunts” generallyincludes the concept of “weak diodes” as used hereafter) during thefabrication process allows them to be electrically isolated, whichincreases the efficiency of the photovoltaic material 12. The electricalisolation of the shunts can be accomplished by laser ablation, forexample, to remove the transparent conducting oxide layer or backcontact material in a ring enclosing the shunt or, for the case ofshunts located close to the edge of the photovoltaic material, byenclosing the shunt using both the edge of the photovoltaic material andan ablated region that intersects the edge of the material on eitherside of the shunt. The shunt position, and other useful information suchas shunt resistance, as well as information on position and energy levelof any recombination centers, and local characterization of areas ofreduced carrier mobility can also be used to provide feedback formaterial deposition and general process control during fabrication ofthe photovoltaic 12.

An optical beam 14 induced current scan of the film 12 that is performedafter the final transparent conductive oxide contact is applied to thefilm 12 is generally sensitive to substantially all shunts beneath theconducting contact, not only the shunt closest to the light beam 14.This greatly reduces the signal to noise level of the measurement.However, various embodiments of the present invention detect localizedshunting defects in thin films 12 by measuring the photoelectric yieldfrom the surface of the photovoltaic 12 before application of the finalcontact layer by using an ultraviolet laser 14 c, as depicted in FIG. 3.This ultraviolet laser is called the probe laser 14 c. The scan of thephotovoltaic material 12 by the probe laser 14 c may be assisted bysimultaneous illumination of the probed region with a visible laser,called the pump laser 14 d.

The ultraviolet laser 14 c in one embodiment is held at a high enoughenergy to excite electrons from the conduction band minimum to thevacuum, but at an energy that is too low to excite electrons from thetop of the valence band maximum to the vacuum. The pump laser 14 d inthis embodiment is held at a high enough energy to excite electrons fromthe valence band to the conduction band, but at an energy that is toolow to excite electrons from the conduction band to the vacuum.

In one embodiment, the probe laser 14 c is a 266 nanometer, 4.66electron Volt, frequency quadrupled YAG laser, and the pump laser 14 dis a 532 nanometer, 2.33 electron Volt, frequency doubled YAG laser. Theintensity of the pump laser 14 d is much greater than the intensity ofthe probe laser 14 c in this embodiment, so that most of thephotoelectrons are excited to the conduction band by the pump laser 14 drather than by the probe laser 14 c.

This method could be applied, by way of example, to a thin (four micron)film of CdTe deposited on glass—a typical superstrate configuration CdTesolar cell-just before deposition of the final conducting film as a backcontact. The ultraviolet probe laser 14 c scans the CdTe surface 12 in adark room. It incites the ejection of photoelectrons from the top fiveto ten nanometers of the CdTe material 12. Because the energy of theprobe laser 14 c is not high enough to excite electrons from the valenceband at 5.78 electron Volts, only the electrons that are initiallyexcited by the probe 14 c from the valence band to states in theconduction band at 4.28 electron Volts are ejected as photoelectrons.For sufficiently low intensities of the probe laser 14 c, the count ratefor these photoelectrons is relatively small.

A large population of electrons may be excited to the CdTe conductionband by intense illumination of the film 12 from the opposite side(through the glass substrate) by the visible light pump laser 14 d.These electrons are excited throughout the depth of the film 12, butrelatively few photons reach the top few nanometers of the CdTe 12surface on the opposite side from the glass substrate because of thehigh absorption of visible light by CdTe. Electrons in the conductionband reach the ultraviolet probe 14 c primarily by conduction across theCdTe film 12. In general, the action of the solar cell 12 in thepresence of visible light (such as from the pump laser 14 d) conductsthe electrons away from the ultraviolet probe 14 c and towards the glass(on the bottom of the material 12). However, in the presence of a shunt,the electrons conduct in the opposite direction, towards the ultravioletprobe 14 c, where some are ejected as photoelectrons, and thereby serveto complete a circuit through an ammeter (not depicted in FIG. 3) thatis connected to the detector. Hence, an elevated ammeter reading duringthe scan indicates the presence of a shunt in the photovoltaic film 12.FIG. 5 depicts both the flow of electrons in the presence of a shunt,and in normal operation of the photovoltaic 12.

Because the back contact of the film 12 has not yet been deposited onthe CdTe surface, the shunts are generally electrically isolated fromone another by the high resistivity of the CdTe film 12, so that theprobe 14 c is only sensitive to electrical defects directly beneath it.The visible light 14 d, besides pumping electrons to the conduction bandand turning on the open circuit voltage of the solar cell 12, alsoserves to induce a forward bias, and thereby turns on any weak diodesbeneath the probe laser 14 c by means of the open circuit voltagedeveloped across the film 12 in the vicinity of the probe 14 c duringillumination.

For the case of a Cu(In,Ga)Se solar cell 12, the inspection procedure isdifferent because the Cu(In,Ga)Se solar cell 12 is grown in a substrateconfiguration beginning with the opaque back contact. In one embodimentof an inspection process for a Cu(In,Ga)Se solar cell 12, both the probelaser 14 c and the pump laser 14 d are directed to the CdS surfaceopposite the substrate, as depicted in FIG. 4. The CdS film 12 istypically a fifty to one hundred nanometer thick layer deposited on topof the active Cu(In,Ga)Se film, and serves to complete the junction forthe solar cell 12. Substantially all of the photoelectrons ejected bythe ultraviolet probe 14 c are ejected from the CdS film 12. The bandgap of CdS is 2.4 electron volts, which exceeds the 2.33 electron voltenergy of the pump laser 14 d. Hence, electrons are only significantlypumped in the Cu(In,Ga)Se material beneath the CdS film, andpredominantly conduct vertically through the film 12 to the CdS surfacebefore being excited by the ultraviolet probe 14 c. FIG. 6 depicts boththe flow of electrons in the presence of a shunt, and in normaloperation of the film 12.

In general, the action of the solar cell 12 conducts electrons to theultraviolet probe 14 c, such that the photoelectron signal remains high.However, in the presence of a shunt the pumped electrons are conductedin the opposite direction, such that the photoelectron signal is small.Hence, a Cu(In,Ga)Se shunt is detected by a decrease in thesignal—opposite that of the case for CdTe, where a shunt is detected byan increase in the signal.

As for the CdTe case, the inspection is predominantly sensitive toshunts beneath the probe laser 14 c, due to the high resistivity of theCdS film 12. The inspection is preferably performed under vacuum, toallow the photoelectrons to reach the detector. For the cases describedabove, the pump laser may be replaced by any source of light, such as abroad spectrum lamp, that excites electrons between the valence andconduction bands but does not have the energy to excite electrons fromthe conduction band to the vacuum. This could be referred to as a lowerenergy light source, not necessarily in the visible range of thespectrum. The intensity of this light source may be adjusted to vary theopen circuit voltage across the photovoltaic film 12, thereby allowingthe inspection to selectively activate weak diodes that have differentopen circuit voltages. Likewise, the probe laser may be replaced by anylight source, including a broad spectrum lamp, with an energy sufficientto excite electrons from the conduction band minimum to the vacuum. Thiscould be referred to as a higher energy light source.

A vacuum of about one-tenth of a millitorr to about one millitorr iscreated in a chamber mounted to a frictionless air bearing that ispassed over the film 12. Alternately, the film 12 is passed beneath avacuum chamber mounted to a frictionless air bearing, such as in thecase of a moving conducting web on which a Cu(In,Ga)Se film isdeposited. Either the probe laser 14 c or both the probe and pump lasers14 c and 14 d are directed through an ultraviolet quality fused silicawindow 24 that is coated with a transparent conducting oxide film on thesurface that faces the photovoltaic material 12. The separation betweenthe window 24 and the photovoltaic film 12 is reduced to a small enoughgap (such as less than about one millimeter) to allow ejectedphotoelectrons from the photovoltaic film 12 to reach the transparentconducting oxide film, and from there to be conducted to an ammeter (notdepicted in FIG. 4).

The opposite terminal of the ammeter is electrically connected to thesingle conducting contact on the solar cell 12. For CdTe photovoltaics12, the conductor is the transparent conducting oxide layer that isdeposited on the glass substrate. For Cu(In,Ga)Se photovoltaics 12, theconductor is typically the steel substrate on which the Cu(In,Ga)Se isgrown. Electrical contact with the substrate can be made in a variety ofdifferent ways, such as with a conducting brush in the case of a movingweb of material 12.

In one embodiment of this invention, the transparent conducting oxidefilm coating the detector is scribed in the direction of the motion ofthe vacuum chamber or photovoltaic material to create separate detectors28 that are read in parallel, as depicted in FIG. 4. The ultravioletprobe 14 c and the visible pump 14 d are then focused to a streak sourceacross the window 24, normal to the scribe lines 26, so that data iscollected simultaneously from all of the detectors 28.

Thus, use of surface contact methods that are not based on thephotoelectric effect, such as by using a plasma or a brush or, in thecase of electron beam induced current, the electron beam itself (aseither a positive or negative contact, depending on the landing energy),can be used for direct, in-line inspection of the photovoltaic materialusing electron beam induced current or optical beam induced current todetect not only the areas of the shunts, but also regions of poorcarrier collection due to a poorly formed p-n junction, highrecombination, or low mobility. Results from this in-line inspection canbe used for electrical isolation of the shunts, or feedback for controlof the deposition processes or other process steps involved in thefabrication of the photovoltaic device.

If sufficient signal to noise levels are available, two streak sourcesand detectors can be deployed at, for example, nominal angles ofpositive forty-five degrees and negative forty-five degrees with respectto the axis normal to the direction of the moving photovoltaic material12. The position of the defect is then determined by the time of arrivalof the signal at each source. Such a configuration can also be used withoptical sources and segmented detectors to locate other defects besideselectrical shunts. These defects include, for example, regions of poorcarrier collection due to a poorly formed p-n junction, highrecombination, or low mobility due to deviations from idealstoichiometry or defects in the crystal structure or the size of thecrystalline regions, or the presence of contaminants. In addition, thebare substrate can be inspected for scratches or surface contamination(such as organic stains).

Yet another embodiment uses an electron source such as a scanningelectron microscope column or nanotube emitter to complete the circuit.In one embodiment the electron source is rastered across the film in adirection normal to the direction of the moving material 12. The signalis the electron beam induced current that is collected from the contacton the opposite side of the film 12. The landing energy is preferablyvaried to deposit predominantly positive or negative charge, therebyutilizing the electron beam to make electrical contact with the topsurface of the photovoltaic device 12.

The foregoing description of preferred embodiments for this inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Obvious modifications or variations are possible inlight of the above teachings. The embodiments are chosen and describedin an effort to provide the best illustrations of the principles of theinvention and its practical application, and to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

1. A method of inline inspection of photovoltaic material for electricalanomalies without removing samples from the material, the methodcomprising the steps of: applying a first light, called a probe source,to a location of the photovoltaic material, where the probe source isapplied at a probe energy sufficient to emit photoelectrons from aconduction band of the photovoltaic material into a vacuum environment,but the probe energy is insufficient to substantially excite electronsfrom a valence band of the photovoltaic material into the vacuumenvironment, selectively simultaneously applying a second light, calleda pump source, to the location of the photovoltaic material, where thepump source is applied at a pump energy sufficient to excitephotoelectrons from the valence band of the photovoltaic material to theconduction band, but the pump energy is insufficient to substantiallyemit photoelectrons from the conduction band of the photovoltaicmaterial into the vacuum environment, sensing the photoelectrons thatare excited into the vacuum environment to measure a current, andinterpreting fluctuations in the current as electrical anomalies.
 2. Themethod of claim 1, wherein the photovoltaic material does not include acontact layer at the location of the application of the probe source. 3.The method of claim 1, wherein the probe source is applied to a firstside of the photovoltaic material and the pump source is applied to asecond side of the photovoltaic material.
 4. The method of claim 1,wherein both the probe source and the pump source are applied to a firstside of the photovoltaic material.
 5. The method of claim 1, wherein theprobe source and selectively the pump source are applied to a first sideof the photovoltaic material through a transparent port into the vacuumenvironment, where an interior surface of the transparent port is coatedwith a transparent conductive material that is disposed in proximity tothe photovoltaic material sufficient to receive and sense thephotoelectrons emitted from the photovoltaic material.
 6. The method ofclaim 1, wherein the probe source and selectively the pump source areapplied to a first side of the photovoltaic material through atransparent port into the vacuum environment, where an interior surfaceof the transparent port is coated with a transparent conductive materialthat is disposed in proximity to the photovoltaic material sufficient toreceive and sense the photoelectrons emitted from the photovoltaicmaterial, and the transparent conductive material is disposed insections on the transparent port, where the sections are electricallyisolated one from another, thereby enabling separate measurement of theemitted photoelectrons based on a position of the photovoltaic materialfrom which the photoelectrons are emitted.
 7. The method of claim 1,wherein the vacuum environment is formed within a chamber formed againstthe photovoltaic material with a frictionless air bearing that allowsthe photovoltaic material to pass freely beneath the chamber.
 8. Themethod of claim 1, wherein a pump intensity is variable, and selectivelychanges an open circuit voltage across the photovoltaic material at thelocation, thereby selectively activating weak diode defects in thephotovoltaic material that have different open circuit voltages.
 9. Themethod of claim 1, wherein the pump source is applied so as to exciteelectrons to the conduction band in portions of the photovoltaic filmthat are not limited to the location, thereby using a conductivity ofthe photovoltaic film to transport the electrons excited by the pumpsource to the location.
 10. The method of claim 1, wherein theinspection of the photovoltaic film is performed before a finalconducting film is applied to the photovoltaic film.
 11. The method ofclaim 1, wherein at least one of the pump energy and the probe energy isvaried to selectively excite electrons to at least one of the conductionband and the vacuum respectively, in portions of the photovoltaic filmthat are not limited to the location.
 12. The method of claim 11,wherein scattered light is detected to detect surface anomalies.